Dual channel magnetic recorder and method



Dec. 5, 1950 H. A. HOWELL 2,532,917

DUAL CHANNEL MAGNETIC RECORDER AND METHOD Fil ed Oct. 18, 1945 I Hue/h4- Hon/11.

Patented Dec. 5, 1950 DUAL CHANNEL MAGNETIC RECORDER AND 'METHOD Hugh A. Howell, Valparaiso,--Ind.,.assignor to The I Indiana Steel Products Company, Chicago, 111., a corporation of Indiana Application October 18, 1946, Serial No. 7045036 6 Claims. 1 This invention relates to a dual channel magnetic recorder and method, and more particularly, to a novel method and means for magnetic recording in which the normal audio range is separated into two bands for independent, si- 5 and a lower band and to bias the upper band by multaneous recordings on dual tracks, but in direct current and :the lower band by high irewhich theilow band is recorded with a superimquency'currentdurlng the recording process.

posed high frequency bias and in which the high The novel features which I believe to be charrange isirecorded with aD. C. biasr acteristic of my invention are set forth with It has been determined that the relatively low particularity in (the .appended claims. My invennotes of the audio range are much better r tion itself, however, both as to its organization, corded in any magnetic recording process when manner of construction and method of operaa high frequency bias i employed w t tion, together with further objects and advan-' term high frequency bias is employed, it is tages thereof may best be understood by refermeant that an additional high frequency signal ence to the following description taken in .conis superimposed on the low frequency signal to nection with the accompanying drawing, in be recorded, the frequency of the high frequency which the single figure thereof is a diagramsignal being sufficiently great that under normal matic illustration of a dual channel magnetic conditions it will not be recorded on the magre rd r em ody t novel t a in an netizable record member. characteristics of the present invention,

It has further been determined that high notes .As shown in the single figure of the drawing. are recorded with greater degree of fidelity and a tape I!) having a pair of magnetizable chanless background noise when themagnetically ponel portions II and I2 is arranged to pass over larized, and preferably saturated, record memthe permanent magnet l before it p ses th ber is passed througha field excited by the audio recording heads 14 and 15 which are associated signal and a superimposed direct current bias, with the tracks H and 12, p t y- The the direction of the direct current bias being magnetic record member It, may, (if C yvar such as to-cause partial demagnetization of the widely Without d p rting from the sp and saturated record member. scope of the present invention. By way of ex- One Of the principal features and objects of pl and s y f lim a h ma the present inventionis'to provide a novel methnetic record member 10 may in th f 10 0d and means for magnetic recording in which a paper tape 16 having -two bands of magnetizaa single tape'having a pair of magnetizable tracks ble material secured "thereon to form two magthereon 'is first passed through a strong D. C. netiza'ble Channel's and biasing field which substantially saturates the These ch nnels II and 12 maybe formed ofma netizabl -t k on th tape, in which suitable powdered magnetizable material :having the tracks are thereafter passed through 'a pair relatively high f? fore? and cemented :to of fluctuating "magnetic fields, respectively, one melt-ape e a bmder' of which is excited by the audio signals below a 40 1 saifllratmg mignet somgtlmes called predetermined point in the audio range with a ig gg g zii gggz f ggg g g g g fi q i z s g g g i fig g ggg g g i s gi gigs: lying therebetween. The gap l9 extends transp d to t d d b verse to the direction of travel of the magnetic i e an lass y i record-member m. :It will be noted that the perdlrectlomfl magnemzlrtg fie1d cmpnem Opposlte manent magnet 13 is sufficiently wide so as to to that or the saturatmg fieldextend across both channels or tracks H and 12.

A further obiect of the present invention is It is also to be understood that the permanent to p ov d a novel dual channel magnetic magnet I3 is :sufficiently strong so as to either cording device and method. substantially saturate the tracks I! and l2 in a Another objector the present invention is to v longitudinal direction, or at least to raise them provide a novel method of feeding energy to the recording means of a magnetic recorder.

- A still further object of the present invention is to separate the signal into an upper band to a uniform magnetic potential level which is at least as high as the highest previously recorded signal.

The input circuit representing the means for picking up the signal to be recorded is diagrammatioally represented as a microphone 20. The microphone is connected to the input side of a suitable aud o amplifier 2|. The output of the audio amplifier is connected to a low pass filter represented by the block diagram 22 and also in parallel to a high pass filter represented by the block diagram 23. It is to be understood that the two filters 22.and 23 are arranged to separate the signal picked up by the microphone 28 into two frequency bands, a low band and a high band. For example, the two filters may be so arranged that the filter 22 passes only signals below 1,000 cycles per second, while the filter 23 passes only signals above 1000 cycles per second. While this point of separat on as between the low band and the high band may vary to a considerable extent without departing from the spirit and scope of my invention, it has been found from a practical standpoint exceptiona ly good results may be obtained by making this point somewhere between 800 and 1,000 cycles.

The output side of the low pass filter 22 is connected to the head I4, while the output of the high pass filter 23 is connected to the recording head l5.

As previously indicated, the low frequency band is to be recorded with the use of a high frequency bias. This is obtained by taking the out-- put of a suitable high frequency oscil'ator 24 and connecting it through a condenser 25 to the head circuit of the head l4. The condenser 25 prevents the low frequency signals from being fed back into the oscillator 24.

In order to keep the high frequency bias out of the filter 22 and the amplifier 2 l, a choke coil 26 is preferably emp7oyed in the circuit between the oscillator connection and the low pass filter 22.

The higher band of audio signal wh ch is fed to the recording head 15 receives a D. C. bias by means of a bias battery 21 connected in the head circuit of the head l5. It will be understood that the bias battery 27 is connected into the circuit in such a manner that its D. C. component sets up a magnetic field component tending to part ally demagnetize the track l2. In other words, this ma netic field component established by the bias battery 21 is in a direction opposite to that of the polarizing field created by the permanent ma net l3. While a battery 21 is shown as providing this partial demagnetizing magnetic field component, it will, of course, be understood that this component may be provided by any suitable e ectric or magnetic means without departing from the spirit and scope of the present invention.

Insofar as the frequency of the oscil ator 24 is concerned, this is preferably relatively high, for it has been found that the h gher the high frequency bias field is in any head, the purer the low frequency response is and the higher the energy level is which may be recorded without distortion.

1 Where, as in the past, the high frequency bias field has been employed with only a single recording head, it has been noted that by increasing the high frequency bias, you progressively lessen the high frequency response. It will, therefore, be apparent that by eliminating the use for the high frequency bias for the higher frequencies, the beneficial effect of a real high high frequency bias may be employed in order to greatly improve the quality of the low frequency response. The high frequency response is made relatively pure and efficient in the present novel recorder and method by employing a D. C. bias.

It will, of course, be apparent that a relatively low frequency bias may be employed for the higher signal band rather than a D. C. bias in conjunction with a relatively high high frequency bias for the lower signal band.

While I have shown a certain, particular embodiment of my invention, it will, of course, be understood that I do not wish to be limited thereto, and I. therefore, contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

I claim as my invention:

1. A magnetic recorder comprising a dual magnetizable track record member, a polarizing head for substantially magnetically saturating said tracks, a pair of recording heads, one associated with each track, a signal input ciriuit, filter means for separating an input signal into a lower and an upper band, means for feedin said lower band to one of said heads and said upper band to the other of said heads, means for superimposing a high frequency signal on said lower band as it is fed to its associated head, and means for superimposing a D. C. bias on said upper band as it is fed to its associated head.

2. A magnetic recorder comprising a dual magnetizable track recorder member, a polarizing head for substantially magnetically saturating said tracks, a pair of recording heads, one associated with each track, a signal input circuit. filter means for separating an input signal into a lower band and an upper band, means for feeding said lower band to one of said heads and said upper band to the other of said heads, means for superimposing a high frequency signal on said lower band as it is fed to its associated head, and means for superimposing a D. C. bias on said upper band as it is fed to its associated head, the D. C. biasing component being such as to tend to establish a magnetic field opposite to that of said saturating magnet.

3. A ma netic recorder comprising a dual magnetizable track record member, polarizing means substantially saturating said tracks in a direction longitudinally of said record member, a pair of recording heads for establishing fluctuating magnetic fields whose respective magnetic axes lie parallel to the longitudinal axis of said record member, one of said heads being associated with one of said tracks and the other of said heads being associated with the other of said tracks, a signal input circuit, a low pass filter and a high pass filter connected in parallel to the output of said signal input circuit, said low pass filter being connected to one of said recording heads and said high pass filter being connected to the other of said recording heads, a high frequency oscillator connected to said recording head associated with said low pass filter, and a D. C. bias battery connected in the head circuit of said high pass filter, the direction of the D. C. biasing force being such as to tend to create a magnetic field to partially demagnetize the track associated with the head connected to the high pass filter.

4. The method of magnetic recording which includes separating the signal to be recorded into a lower band and an upper band and then simultaneously subjecting a first magnetizable record member to said lower band and a superimposed high frequency bias current and a second mag netizable record member to said upper band and a superimposed direct current bias.

5. The method of magnetic recording on a dual track magnetic record member which includes the steps of first magnetically saturating said tracks and then subjecting one of said tracks to a high frequency magnetic field and a predetermined low frequency portion of the signal to be recorded and the other track to the remaining portion of said signal and a uni-directional magnetic field.

6. The method of magnetic recording which includes separating the signal to be recorded into two bands, creating a fluctuating magnetic field with each band, and then recording with the magnetic field of the low band with a high frequency magnetic field superimposed thereon, and

2 simultaneously recording with the magnetic field June 1946.

of the upper band with a uni-directional magnetic field superimposed thereon.

HUGH A. HOWELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number OTHER REFERENCES An Appraisal of Design Trends in Magnetic Sound Recorders, Electrical Manufacturing,

(Copy in Div. 16.) 

